This invention relates to film substrates that are used as an ink receptive print media and, more particularly to non-topcoated film substrates having at least one ink receptive surface, constructions such as labels and labelstocks incorporating such film substrates, and methods for preparing the same.
Ink jet printing is a well-known and commonly used means of providing an image onto a substrate. Ink jet printers typically use one of two different types of ink; dye-based inks and pigment-based inks. With dye-based ink, the color of the ink is imparted by a dye that is soluble in a fluid carrier. A common type of fluid carrier is one comprising a blend of water and glycol. Such dye-based inks are relatively inexpensive, easy to process, and are suitable for use in low cost applications where long term durability is not a concern. For pigment-based inks, the color is imparted by particles which are dispersed, rather than dissolved, in a fluid carrier. Most of the common pigments used are insoluble in organic solvents and water can be chosen for lightfastness.
A feature common to both types of inks is that the fluid carrier used with each is generally water soluble. Thus, substrates useful for performing as an inkjet receiving media preferably comprise a surface having ink receptive properties to allow quick drying of ink droplets generated by an inkjet print head. Substrates known in the art useful as an inkjet receiving media include those having a two-layer construction comprising a base layer and a topcoat layer. In such known substrate embodiments, the base layer is formed from a polymeric film such as polypropylene, polyester, or polyvinyl chloride. The topcoat layer is applied to a surface of the base layer, using a solvent that is subsequently removed by drying, and is specially formulated to provide ink receptive properties.
However, the use of a topcoat to provide ink receptive properties to a substrate is known to introduce certain manufacturing limitations, and adversely affect other substrate properties that can ultimately limit ink printed substrate use. For example, topcoated inkjet substrates are known to lack durability and, because most topcoat formulations contain water-soluble components, they are also sensitive to moisture, thereby necessitating the use of a protective overlaminate layer or film after printing. Additionally, the level of active components in the topcoat formulation is limited by the viscosity of the topcoat formulation that can be handled in the coater. As a result, the efficiency of the topcoat is commonly increased by increasing the layer thickness, which is known to introduce increased costs and coat weight inconsistencies, which inconsistencies are undesirable because they can adversely affect the performance of the final product, i.e., the ink jet printed substrate.
In an effort to avoid the above-mentioned adverse consequences of topcoated substrates, non-topcoated substrates having varying degrees of ink receptive properties have been developed. For example, U.S. Pat. No. 4,438,175 discloses a film structure comprising a biaxially-oriented polymeric film having an ink receptive surface that is formed by delaminating the biaxially-oriented polymeric film into two separate layers, each of which being attached to a skin layer. The resulting polymeric film structure comprises a first layer of a thermoplastic polymer matrix material comprising a strata of voids. Void-initiating solid particles are positioned within a substantial number of the voids and are phase distinct and incompatible with the matrix material. The first layer has a surface that, due to the presence and distribution of voids, is a non-even, microcrater, lamellae-like, random texturized, ink receptive configuration. The resulting polymeric film includes a second layer, formed by the placement of the skin layer onto the matrix, having a void-free surface.
While this patent discloses a substrate having an ink receptive surface that is formed without topcoating, the so formed substrate requires a two-step manufacturing process of first forming the combined polymeric film and skin layer construction, and then delaminating the combined film and skin layer construction into two resulting ink receptive film structures. Thus, while the substrate described in this patent avoids having to use a topcoating method, it does not avoid the inefficiencies and costs associated with having to use multiple preparation steps.
U.S. Pat. No. 4,861,644 describes a substrate having an ink receptive surface comprising a matrix of ultrahigh molecular weight polyolefin, a large proportion of finely-divided water-insoluble siliceous filler, and interconnecting pores. The substrate is produced by first forming an extruded sheet from a mixture of the polyolefin the siliceous filler and other processing aids, calendaring the extruded sheet, drying the calendared sheet, and stretching the dried sheet to provide a desired biaxially stretched orientation. While the so formed substrate also avoids the need for topcoating to obtain ink receptive properties, the substrate is nevertheless formed using the multi-step process of extruding, calendaring, drying and stretching.
International Publication No. WO 92/00188 discloses a writeable and printable, unstretched synthetic paper that is formed by extruding a film with a continuous olefin resin matrix that contains an effective amount of particulate filler having inherent microvoids. The microvoid-containing particulate filler is dispersed uniformly and randomly throughout the continuous olefin resin matrix to provide non-mechanically produced microvoids in communication with the surface pores to provide ink receptivity thereto. The synthetic paper of this patent is formed by extruding a mixture of the olefin resin matrix and particulate filler into a desired sheet thickness. While the so-formed substrate avoids the step of topcoating to achieve an ink receptive surface structure, it relies on the formation of a porous or voided surface structure that can be the source of performance limitations.
International Publication No. WO 92/00188 discloses an inkjet printable microporous ethylene-vinyl alcohol copolymer film that is formed by melt blending a mixture of ethylene-vinyl alcohol copolymer and a compatible polymer or compound in which the copolymer will dissolve to form a solution at its melting temperature. The solution is formed into a film, which is cooled. During the cooling step, a phase separation occurs between the compatible copolymer or compound and the ethylene-vinyl alcohol polymer, providing a film comprising an aggregate of a first phase particles of ethylene-vinyl alcohol copolymer in a second phase of the compatible polymer or compound. The cooled film is collected, the compatible polymer or compound is extracted, and the resulting film is stretched. Micropores are formed in the film structure by extracting the compatible polymer or compound therefrom. While the substrate formed according to this publication avoids the step of topcoating to achieve an ink receptive surface structure, like the other above-described non-topcoating methods, it also relies on the formation of a porous or voided surface structure that can be the source of performance limitations.
The common theme of the above described non-topcoated ink receptive substrates is that they each depend on use of a voided or porous substrate surface to provide a surface structure that is receptive to ink deposited thereon. The use of a substrate surface having such a voided or porous structure, however, is not without its limitations. For example, it is known that such substrates can suffer from poor image quality. Substrates having such surface structures tend to act like a sponge, absorbing ink deep into the substrate body, often resulting in poor color densities and resolutions. These substrates are also prone to provide poor optical qualities as the surface voids oftentimes provides a surface that is mostly opaque or translucent, thereby limiting potential substrate applications. Additionally, substrates having such voided surface structures oftentimes require a complex manufacturing process. For example, it is not unusual for such substrates to have a complex material formulation and/or multiple process steps, which can add both to the expense and time associated with making the substrate.
For these reasons, it is desired that an ink receptive substrate be constructed that both avoids the need for topcoating, and that avoids reliance on a voided microstructure, i.e., that is xe2x80x9cinherentlyxe2x80x9d ink receptive. It is desired that such inherently ink receptive substrates provide properties of image quality and optics that are superior to those provided by substrates having voided microstructures. It is desired that such inherently ink receptive substrates be fabricated in a manner that avoids the need for multiple time consuming and costly process steps. It is further desired that inherently ink receptive substrate constructions of this invention be capable of receiving ink as deposited by inkjet technique, as well as by other methods of ink transfer.
Ink receptive substrates of this invention comprise a base layer formed from a water-insoluble thermoplastic polymer, and an ink receptive layer disposed over the base layer. The ink receptive layer is formed from a melt processable blend of a water-soluble polymer and a substantially water-insoluble polymer, and provides an inherently ink receptive surface without further surface treatment. A tie layer can optionally be interposed between base and ink receptive layer.
The base layer is selected from the group of thermoplastic material consisting of polyolefins, polyesters, polyurethanes, polyvinyl chlorides, polyamides, polystyrene, ethylene vinyl alcohol, and mixtures thereof. The ink receptive blend comprises in the range of from 20 to 80 percent by weight water-soluble polymer, and in the range of from 20 to 80 percent by weight substantially water-insoluble polymer based on the total weight of the blend. The blend may include an optional compatibilizing agent that is chemically compatible with both the water-soluble polymer and the substantially water-insoluble polymer.
The blend has a melting temperature in the range of from about 100 to 600xc2x0 F. The water-soluble polymer component of the blend is selected from the group of compounds consisting of polyvinyl alcohols, polyalkyl oxazolines, polyphenyl oxazolines, polyvinyl pyrrolidones, polyacrylic-acids, polymethyl methacrylates, polymethacrylic acids, styrene maleic anhydrides, alkyl celluloses, carboxyalkyl celluloses, hydroxyalkyl celluloses, polyethylene oxides, polyethylene-imines, and mixtures thereof.
Preferred water-soluble polymers include polyalkyl oxazoline and polyvinyl alcohol. The substantially water-insoluble polymer component of the blend is selected from the group of polyolefins consisting of modified and unmodified polyesters, polypropylenes, polyethylenes, polystyrenes, polybutylenes, and copolymers and mixtures thereof.
In a preferred embodiment, the base layer and ink receptive layer of ink receptive substrates of this invention are formed simultaneously by coextrusion process. Ink receptive substrates of this invention can include the ink receptive layer on one or both surfaces of the base layer, and/or can be constructed in the form of a pressure-sensitive adhesive label, i.e., with a pressure-sensitive adhesive material disposed on a surface of the base layer opposite the ink receptive layer.
Ink receptive substrates of this invention are inherently ink receptive in that they avoid that need for topcoating or reliance on a voided microstructure to gain ink receptivity. Ink receptive substrates of this invention provide properties of image quality and optics that are superior to those provided by substrates having voided microstructures. Ink receptive substrates of this invention are fabricated in a manner that avoids the need for multiple time consuming and costly process steps.